1. Field of the Invention
The present invention relates to a technique for manufacturing a semiconductor device, and more particularly to a technique to reduce defective film formation.
2. Description of the Background Art
FIGS. 68 and 69 are a plan view and a cross section, respectively, showing an exemplary structure of an AND-type flash memory. FIG. 69 is the cross section taken along the position Q1xe2x80x94Q1 of FIG. 68.
For example, in a surface of a silicon substrate 1, element formation regions are insulated from one another by a plurality of trench isolation oxide films 2. On a surface of the element formation region, sources 3a and 18a serving as a source line and drains 3b and 18b serving as a bit line are formed, being spaced from one another. The sources 3a and 18a and the drains 3b and 18b are extended almost in parallel to one another in a longitudinal direction of FIG. 68. A plurality of control gates 8 serving as word lines are formed in a traverse direction of FIG. 68, being insulated from one another. The position Q1xe2x80x94Q1 is determined along the control gates 8.
On the sources 3a and 18a, the drains 3b and 18b and the trench isolation oxide films 2, an oxide film made of TEOS (Tetra Ethyl Ortho Silicate: Si(C2H5O)4) (hereinafter referred to as xe2x80x9cTEOS oxide filmxe2x80x9d) is formed as a thick insulating film 6. A channel region 1a is located in a region of the silicon substrate 1 sandwiched between the sources 3a and 18a and the drains 3b and 18b. A floating gate 5 is formed over the channel region 1a with a tunnel oxide film 4 interposed therebetween. On the floating gate 5, a phosphor-doped amorphous silicon film 9, an ONO (Oxide-Nitride-Oxide) film 7 and a control gate 8 are layered in this order. The control gate 8 includes a polysilicon film 8a and a tungsten silicide film 8b formed thereon.
A silicon oxide film 11 is formed as an insulating film on the control gate 8. Further on the silicon oxide film 11, an interlayer insulating film 21 is formed. Memory cell transistors (Tr1, Tr2, . . . ) each include the sources 3a and 18a, the drains 3b and 18b, the floating gate 5 and the control gate 8. In order to read information stored in the transistor Tr2, a predetermined voltage is applied to the sources 3a and 18a and a predetermined voltage is applied to the control gate 8 corresponding to the transistor Tr2. At this time, whether the transistor Tr2 is turned on or not depends on the amount of electrons accumulated in the floating gate 5 of the transistor Tr2. When the transistor Tr2 is turned on, currents flow between the sources 3a and 18a and the drains 3b and 18b. 
A plurality of memory cell transistors Tr1, Tr2, . . . share the sources 3a and 18a and the drains 3b and 18b, and are connected in parallel to one another to constitute an AND-type flash memory.
In a flash memory, there are capacitance between the floating gate 5 and the silicon substrate 1 (mainly consisting of the capacitance of the tunnel oxide film 4: hereinafter referred to as xe2x80x9cfirst gate capacitancexe2x80x9d) and capacitance between the floating gate 5 and the control gate 8 (hereinafter referred to as xe2x80x9csecond gate capacitancexe2x80x9d). Generally required is a flash memory which allows fast write and fast erase to/from memory cells. To satisfy this requirement, it is desirable that the second gate capacitance should be stably larger than the first gate capacitance.
Specifically, it is required that the film thickness of the ONO film 7 should be thin, allowing excellent repeatability and uniformity. For example, a target value of film thickness for each of a bottom silicon oxide film (closer to the silicon substrate 1), a silicon nitride film and a top silicon oxide film (away from the silicon substrate 1) constituted of the ONO film 7 is about 5 nm, aiming for a very thin thickness. Very strict film characteristics are required, that variation of film thickness obtained in one process (one batch) should be within the target value xc2x15% or lower with excellent repeatability.
An object of the present invention is to provide a technique for film formation with film thickness easily controlled in the chemical vapor deposition method, for example, a technique applicable to a case where a silicon oxide film such as the bottom silicon oxide film of the ONO film 7 is formed on a semiconductor substrate on which a TEOS oxide film such as the thick insulating film 6 exists. As obviously can be seen from the following preferred embodiments, however, the present invention is intended not only for use in film formation of an oxide film but also for use in other film formation, for example, of a nitride film with its film thickness easily controlled.
The present invention is directed to a method of manufacturing a semiconductor device. According to a first aspect of the present invention, the method of manufacturing a semiconductor device includes steps (a) to (c). In the step (a), a first layer is formed by performing the chemical vapor deposition method on a semiconductor substrate at a first temperature and a first pressure for a first period. In the step (b), a heat treatment is performed under an inert gas atmosphere while exhausting a gas from the vicinity of the semiconductor substrate. In the step (c), a second layer is formed by performing the chemical vapor deposition method at a second temperature and a second pressure for a second period. The second temperature is higher than the first temperature and the second pressure is lower than the first pressure. The heat treatment is performed in the step (b) at a third temperature and a third pressure. The third temperature is equal to or higher than the second temperature and the third pressure is equal to or lower than the second pressure.
The gas used for forming the first layer in the step (a) is desorbed from the first layer in the step (b). Therefore, it is possible to reduce an ill effect of the gas in the film formation of the second layer of the step (c).
According to a second aspect of the present invention, the method of manufacturing a semiconductor device includes steps (a) to (c). In the step (a), a first layer is formed on both a main surface and a back surface of the semiconductor substrate by performing the chemical vapor deposition method on the semiconductor substrate at a first temperature and a first pressure. In the step (b), the first layer formed on the back surface is removed. In the step (c), a second layer is formed by performing the chemical vapor deposition method at a second temperature and a second pressure for a second period. The second temperature is higher than the first temperature and the second pressure is lower than the first pressure.
The ill effect of the gas contained in the first layer, which is used for forming the first layer, on the film formation of the second layer in the step (c) becomes smaller.
According to a third aspect of the present invention, the method of manufacturing a semiconductor device includes steps (a) to (c). In the step (a), a first layer is formed on both a main surface and a back surface of a semiconductor substrate by performing the chemical vapor deposition method on the semiconductor substrate at a first temperature and a first pressure. In the step (b), the first layer formed on the back surface is covered. In the step (c), a second layer is formed by performing the chemical vapor deposition method at a second temperature and a second pressure. The second temperature is higher than the first temperature and the second pressure is lower than the first pressure. The first layer is covered in the step (b) with a film which prevents gas desorption from the first layer in the step (c).
The ill effect of the gas contained in the first layer, which is used for forming the first layer, on the film formation of the second layer in the step (c) becomes smaller.
According to a fourth aspect of the present invention, the method of manufacturing a semiconductor device is a method for forming a first layer and a second layer on a semiconductor substrate in this order. A gas used for forming the first layer is desorbed in forming the second layer. The fourth aspect of the present invention includes steps (a) to (d). In the step (a), obtained is a film formation condition under which the second layer is formed to have a predetermined thickness on a dummy wafer not having the first layer. In the step (b), the second film is formed on the semiconductor substrate having the first layer under the film formation condition obtained in the step (a). In the step (c), the film formation condition is modified on the basis of the thickness of the second layer actually formed in the step (b). In the step (d), the second layers are formed on the dummy wafer not having the first layer and subsequently on the semiconductor substrate having the first layer under the film formation condition modified in the step (c).
The ill effect of desorption of the gas used for forming the first layer on the film formation of the second layer is estimated in the step (c). Therefore, it is possible to form the second layer with a predetermined film thickness on the semiconductor substrate, subsequently to the dummy batch, in the step (d).
The present invention is directed to a method of determining a film formation time. According to a fifth aspect of the present invention, the method is to determine a film formation time in a film formation process performed on a semiconductor substrate on which a semiconductor device is materialized. The fifth aspect of the present invention includes steps (a) to (d). In the step (a), obtained is wafer information on the type of semiconductor device and process steps which have been performed on the semiconductor substrate before the film formation process. In the step (b), a film structure that the semiconductor substrate has had before the film formation process is obtained on the basis of the wafer information. In the step (c), whether gas desorption should occur or not in the film formation process is predicted on the basis of the film structure and the details of the film formation process. In the step (d), a film formation time in the film formation process is determined on the basis of the result of the step (c).
It is possible to determine the film formation time for obtaining a predetermined film thickness, regardless of whether gas desorption occurs or not.
The present invention is still directed to a chamber. According to a sixth aspect of the present invention, the chamber has an upper surface, a lower surface, a gas introduction port and a gas exhaust port. The upper and lower surfaces are translucent. The lower surface has lift pins and an exhaust hole.
Since lamp annealing can be performed from both the upper surface and the lower surface and the wafer can be supported by the lift pins, a rapid thermal annealing is performed on both sides of the wafer. Further, the gas desorbed from the wafer can be efficiently exhausted from the exhaust hole.
The present invention is yet directed to a boat of a chemical vapor deposition apparatus. According to a seventh aspect of the present invention, the boat includes at least one body, a protrusion piece and an exhaust pipe. The at least one body is extended and has a first opening. The protrusion piece is supported by the at least one body. The exhaust pipe conducts to the first opening.
The first opening is located near the semiconductor substrate to be subjected to the chemical vapor deposition, which is placed on the protrusion piece. Therefore, the gas desorbed from the semiconductor substrate is exhausted from the exhaust pipe in parallel to the chemical vapor deposition.
The present invention is further directed to a chemical vapor deposition apparatus. According to an eighth aspect of the present invention, the chemical vapor deposition apparatus includes a reaction pipe, a pressure vessel, a first base, a second base, a boat and a heat source. In the reaction pipe, chemical vapor deposition is performed. The pressure vessel conducts to the reaction pipe, and allows exhaustion. The first base is movable, which allows the pressure vessel to be sealed when comes into contact with the pressure vessel. The second base is movable from the first base to the reaction pipe, and closes the reaction pipe when comes into contact with the reaction pipe. On the boat, mounted is a semiconductor substrate which is subjected to the chemical vapor deposition. The boat moves together with the second base to enter the reaction pipe. The heat source is placed at the position of the pressure vessel away from the reaction pipe.
The annealing is performed by using the heat source in the exhausted pressure vessel immediately before the chemical vapor deposition is performed in the reaction pipe on the semiconductor substrate placed on the boat. Therefore, the method of manufacturing a semiconductor device of the first aspect of the present invention can be carried out for a short time.
The present invention is furthermore directed to an etching apparatus. According to a ninth aspect, the etching apparatus includes a chamber and a ring-like susceptor. The chamber has two surfaces opposed to each other. The ring-like susceptor is mounted on one of the two surfaces. An etching is performed by using plasma generated between the two surfaces.
The semiconductor substrate""s surface that is supported by the susceptor, is not exposed to plasma. Therefore, while the surface is protected, etching is performed on the other surface of the semiconductor substrate.
According to a tenth aspect, the etching apparatus includes a rotation mechanism, a first supply unit and a second supply unit. The rotation mechanism rotates a semiconductor substrate. The first supply unit supplies a liquid etchant to one surface of the semiconductor substrate. The second supply unit sprays a gas to the other surface of the semiconductor substrate.
When one surface is etched, it is possible to prevent the etchant from going around to the other surface.
The present invention is also directed to a film formation process system. According to an eleventh aspect, the film formation process system includes a film formation apparatus, a data base and a control body. The film formation apparatus performs a film formation process on a semiconductor substrate on which a semiconductor device is materialized. The database stores the history of the film formation process. The control body sends and receives information to/from the database to determine a time for the film formation process on the basis of a film structure of the semiconductor substrate and the history of the film formation process.
It is possible to predict whether gas desorption depending on the film structure occurs or not in the film formation process and automatically determine the film formation time for obtaining a predetermined film thickness from the history of the film formation process.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.